Method and apparatus for transmitting and receiving control information to randomize inter-cell interference in a mobile communication system

ABSTRACT

Methods and apparatus are provided for transmitting control information in an SC-FDMA system. A UE generates a random cyclic shift value based on an SC-FDMA symbol index and a slot index. The UE cyclically shifts a sequence by the random cyclic shift value. The UE multiplies a control channel signal, including the control information, by the cyclically shifted sequence on an SC-FDMA symbol basis. The UE transmits the multiplied control channel signal in an SC-FDMA symbol to a Node B.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 11/970,358, filed on Jan. 7, 2008, which claimspriority to a Korean Patent Application filed in the Korean IntellectualProperty Office on Jan. 5, 2007 and assigned Serial No. 2007-1329, aKorean Patent Application filed in the Korean Intellectual PropertyOffice on Jan. 10, 2007 and assigned Serial No. 2007-3039, and a KoreanPatent Application filed in the Korean Intellectual Property Office onMay 10, 2007 and assigned Serial No. 2007-45577, the entire disclosuresof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a mobile communicationsystem. More particularly, the present invention relates to a method andapparatus for transmitting and receiving control information torandomize inter-cell interference caused by UpLink (UL) transmission ina future-generation multi-cell mobile communication system.

2. Description of the Related Art

In the field of mobile communication technologies, recent study in thearea of Orthogonal Frequency Division Multiple Access (OFDMA) or SingleCarrier-Frequency Division Multiple Access (SC-FDMA) reveals verypromising for high-speed transmission on radio channels. Theasynchronous cellular mobile communication standardization organization,3^(rd) Generation Partnership Project (3GPP) is working on afuture-generation mobile communication system, Long Term Evolution (LTE)in relation to the multiple access scheme.

The LTE system uses a different Transport Format (TP) for UpLink controlinformation depending on data transmission or non-data transmission.When data and control information are transmitted simultaneously on theUL, they are multiplexed by Time Division Multiplexing (TDM). If onlycontrol information is transmitted, a particular frequency band isallocated for the control information.

FIG. 1 illustrates a transmission mechanism when only controlinformation is transmitted on the UL in a conventional LTE system. Thehorizontal axis represents time and the vertical axis representsfrequency. One subframe 102 is defined in time and a Transmission (TX)bandwidth 120 is defined in frequency.

Referring to FIG. 1, a basic UL time transmission unit, subframe 102 is1 ms long and includes two slots 104 and 106 each 0.5 ms long. Each slot104 or 106 is comprised of a plurality of Long Blocks (LBs) 108 (or longSC-FDMA symbols) and Short Blocks (SBs) 110 (or short SC-FDMA symbols).In the illustrated case of FIG. 1, a slot is configured so as to havesix LBs 108 and two SBs 110.

A minimum frequency transmission unit is a frequency tone of an LB and abasic resource allocation unit is a Resource Unit (RU). RUs 112 and 114each have a plurality of frequency tones, for example, 12 frequencytones form one RU. Frequency diversity can also be achieved by formingan RU with scattered frequency tones, instead of successive frequencytones.

Since LBs 108 and SBs 110 have the same sampling rate, SBs 110 have afrequency tone size twice larger than that of LBs 108. The number offrequency tones allocated to one RU in SBs 110 is half that of frequencytones allocated to one RU in LBs 108. In the illustrated case of FIG. 1,LBs 108 carry control information, while SBs 108 carry a pilot signal(or a Reference Signal (RS)). The pilot signal is a predeterminedsequence by which a receiver performs channel estimation for coherentdemodulation.

If only control information is transmitted on the UL, it is transmittedin a predetermined frequency band in the LTE system. In FIG. 1, thefrequency band is at least one of RUs 112 and 114 at either side of TXbandwidth 120.

In general, the frequency band carrying control information is definedin units of RUs. When a plurality of RUs is required, successive RUs areused to satisfy a single carrier property. Frequency hopping can occuron a slot basis when frequency diversity for one subframe is increased.

In FIG. 1, first control information (Control #1) is transmitted in RU112 in a first slot 104 and in RU 114 in a second slot 106 by frequencyhopping. Meanwhile, second control information (Control #2) istransmitted in RU 114 in first slot 104 and in RU 112 in second slot 106by frequency hopping.

The control information is, for example, feedback information indicatingsuccessful or failed reception of DownLink (DL) data,ACKnowledgment/Negative ACKnowledgment (ACK/NACK) that is generally 1bit. It is repeated in a plurality of LBs in order to increase receptionperformance and expand cell coverage. When 1-bit control information istransmitted from different users, Code Division Multiplexing (CDM) canbe considered for multiplexing the 1-bit control information. CDM ischaracterized by robustness against interference, compared to FrequencyDivision Multiplexing (FDM).

A Zadoff-Chu (ZC) sequence is discussed as a code sequence forCDM-multiplexing of control information. Due to its constant envelop intime and frequency, the ZC sequence offers good Peak-to-Average PowerRatio (PAPR) characteristics and excellent channel estimationperformance in frequency. PAPR is the most significant consideration forUL transmission. A higher PAPR leads to a smaller cell coverage, therebyincreasing a signal power requirement for a User Equipment (UE).Therefore, efforts should be expanded toward PAPR reduction in ULtransmission, first of all.

A ZC sequence with good PAPR characteristics has a circularauto-correlation value of 0 with respect to a non-zero shift. Equation(1) below describes the ZC sequence mathematically.

$\begin{matrix}{{g_{p}(n)} = \left\{ \begin{matrix}{{\mathbb{e}}^{{- j}\frac{2\pi}{N}\frac{{pn}^{2}}{2}},} & {{when}\mspace{14mu} N\mspace{14mu}{is}\mspace{14mu}{even}} \\{{\mathbb{e}}^{{- j}\frac{2\pi}{N}\frac{{pn}{({n + 1})}}{2}},} & {{when}\mspace{14mu} N\mspace{14mu}{is}\mspace{14mu}{odd}}\end{matrix} \right.} & (1)\end{matrix}$where N is the length of the ZC sequence, p is the index of the ZCsequence, and n denotes the index of a sample of the ZC sequence (n=0, .. . , N−1). Because of the condition that p and N should be relativelyprime numbers, the number of sequence indexes p varies with the sequencelength N. For N=6, p=1.5. Hence, two ZC sequences are generated. If N isa prime number, N−1 sequences are generated.

Two ZC sequences with different p values generated by equation (1) havea complex cross-correlation, of which the absolute value is 1/√{squareroot over (N)} and the phase varies with p.

How control information from a user is distinguished from controlinformation from other users by a ZC sequence will be described, by wayof example.

Within the same cell, 1-bit control information from different UEs isidentified by time-domain cyclic shift values of a ZC sequence. Thecyclic shift values are UE-specific to satisfy the condition that theyare larger than the maximum transmission delay of a radio transmissionpath, thus ensuring mutual orthogonality among the UEs. Therefore, thenumber of UEs that can be accommodated for multiple accesses depends onthe length of the ZC sequence and the cyclic shift values. For example,if the ZC sequence is 12 samples long and a minimum cyclic shift valueensuring orthogonality between ZC sequences is 2 samples, multipleaccesses is available to six UEs (=12/2).

FIG. 2 illustrates a transmission mechanism in which control informationfrom UEs is CDM-multiplexed.

Referring to FIG. 2, first and second UEs 204 and 206 (UE #1 and UE #2)use the same ZC sequence, ZC #1 in LBs in a cell 202 (Cell A) andcyclically shift ZC #1 by 0 208 and Δ 210 respectively, for useridentification. In the illustrated case of FIG. 2, to expand cellcoverage, UE #1 and UE #2 each generate a control channel signal byrepeating the modulation symbol of intended 1-bit UL control informationsix times, i.e. in six LBs and multiplying the repeated symbols by thecyclically shifted ZC sequence, ZC #1 in each LB. These control channelsignals are kept orthogonal without interference between UE #1 and UE #2in view of the circular auto-correlation property of the ZC sequence. Δ210 is set to be larger than the maximum transmission delay of the radiotransmission path. Two SBs in each slot carry pilots for coherentdemodulation of the control information. For illustrative purposes, onlyone slot of the control information is shown in FIG. 2.

In a cell 220 (Cell B), third and fourth UEs 222 and 224 (UE #3 and UE#4) use the same ZC sequence, ZC #2 in the LBs and cyclically shift ZC#2 by 0 226 and Δ 228 respectively, for user identification. In view ofthe circular auto-correlation property of the ZC sequence, controlchannel signals from UE #3 and UE #4 are kept orthogonal withoutinterference between them.

This control information transmission scheme, however, causesinterference between different cells as control channel signals from UEsin the cells use different ZC sequences. In FIG. 2, UE #1 and UE #2 ofCell A use different ZC sequences from those of UE #3 and UE #4 of CellB. The cross-correlation property of the ZC sequences cause interferenceamong the UEs in proportion to the cross-correlation between the ZCsequences. Accordingly, there exists a need for a method for reducinginter-cell interference caused by control information transmission asdescribed above.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least the problemsand/or disadvantages and to provide at least the advantages describedbelow. Accordingly, an aspect of the present invention provides a methodand apparatus for reducing inter-cell interference when controlinformation from different users is multiplexed in a multi-cellenvironment.

Another aspect of the present invention provides a method and apparatusfor further randomizing inter-cell interference by applying acell-specific or UE-specific random sequence to control information in asubframe.

A further aspect of the present invention provides a method andapparatus for notifying a UE of a random sequence applied to controlinformation in a subframe by Layer 1/Layer 2 (L1/L2) signaling.

Still another aspect of the present invention provides a method andapparatus for effectively receiving control information in a subframewithout inter-cell interference.

In accordance with an aspect of the present invention, a method isprovided for transmitting control information in an SC-FDMA system. A UEgenerates a random cyclic shift value based on an SC-FDMA symbol indexand a slot index. The UE cyclically shifts a sequence by the randomcyclic shift value. The UE multiplies a control channel signal,including the control information, by the cyclically shifted sequence onan SC-FDMA symbol basis. The UE transmits the multiplied control channelsignal in an SC-FDMA symbol to a Node B.

In accordance with another aspect of the present invention, a method isprovided for receiving control information in an SC-FDMA system. A NodeB receives a control channel signal, including the control information,from a UE. The Node B generates a random cyclic shift value based on anSC-FDMA symbol index and a slot index. The Node B multiplies the controlchannel signal by a sequence. The Node B acquires the controlinformation by cyclically shifting the multiplied control channel signalby the random cyclic shift value on an SC-FDMA symbol basis.

In accordance with a further aspect of the present invention, anapparatus is provided for transmitting control information in an SC-FDMAsystem. The apparatus includes a control information generator forgenerating the control information. The apparatus also includes asequence generator for generating a random cyclic shift value based onan SC-FDMA symbol index and a slot index. The apparatus further includesa randomizer for cyclically shifting a sequence by the random cyclicshift value. Additionally, the apparatus includes a multiplier formultiplying a control channel signal, including the control information,by the cyclically shifted sequence on an SC-FDMA symbol basis. Theapparatus also includes a transmitter for transmitting the multipliedcontrol channel signal in an SC-FDMA symbol to a Node B.

In accordance with still another aspect of the present invention, anapparatus is provided for receiving control information in an SC-FDMAsystem. The apparatus includes a receiver for receiving a controlchannel signal, including control information, from a UE. The apparatusalso includes a control channel signal receiver for generating a randomcyclic shift value based on an SC-FDMA symbol index and a slot index,multiplying the control channel signal by a sequence, and acquiring thecontrol information by cyclically shifting the multiplied controlchannel signal by the random cyclic shift value on an SC-FDMA symbolbasis.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a transmission mechanism for control information in aconventional LTE system;

FIG. 2 illustrates a transmission mechanism in which control informationfrom UEs is CDM-multiplex;

FIG. 3 is a flowchart of an operation for transmitting controlinformation in a UE according to the present invention;

FIG. 4 is a flowchart of an operation for receiving control informationin a Node B according to the present invention;

FIG. 5 illustrates a transmission mechanism for control informationaccording to the present invention;

FIGS. 6A and 6B are block diagrams of a transmitter in the UE accordingto the present invention;

FIGS. 7A and 7B are block diagrams of a receiver in the Node B accordingto the present invention;

FIG. 8 illustrates a transmission mechanism for control informationaccording to the present invention;

FIG. 9 illustrates another transmission mechanism for controlinformation according to the present invention;

FIGS. 10A and 10B are block diagrams of a transmitter in the MSaccording to the present invention;

FIGS. 11A and 11B are block diagrams of a receiver in the Node Baccording the present invention;

FIGS. 12A and 12B illustrate a transmission mechanism for controlinformation according to the present invention; and

FIG. 13 illustrates another transmission mechanism for controlinformation according to the present invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention are described in detail withreference to the accompanying drawings. The same or similar componentsmay be designated by the same or similar reference numerals althoughthey are illustrated in different drawings. Detailed descriptions ofconstructions or processes known in the art may be omitted to avoidobscuring the subject matter of the present invention.

Embodiments of the present invention provide transmission and receptionoperations of a UE and a Node B in the case where UL control informationfrom a plurality of UEs are multiplexed over a predetermined frequencyarea of a system frequency band.

The present invention will be described in the context of CDMtransmission of control information from a plurality of UEs in anSC-FDMA cellular communication system. Yet, the present invention isalso applicable to multiplexing that does not share particulartime-frequency resources, for example, FDM or TDM transmission of thecontrol information. CDM can be one of various CDMA schemes includingtime-domain CDMA and frequency-domain CDM.

For CDM, a ZC sequence is used, while any other code sequence withsimilar characteristics is available. The control information is 1-bitcontrol information such as ACK/NACK. However, an inter-cellinterference reduction method of the present invention is alsoapplicable to control information with a plurality of bits such as aChannel Quality Indicator (CQI). In this case, each bit of the controlinformation is transmitted in one SC-FDMA symbol. The inter-cellinterference reduction method is also applicable to CDM transmission ofdifferent types of control information, for example, 1-bit controlinformation and control information with a plurality of bits.

Inter-cell interference occurs when UEs in adjacent cells transmit theircontrol information using different ZC sequences of length N in MSC-FDMA symbols, i.e. M LBs being UL time transmission units.

If the phases of the correlations between sequences in LBs from UEswithin adjacent cells are randomized while the circular auto-correlationand cross-correlation properties of the ZC sequence are maintained, thephase of interference between the adjacent cells is randomized acrossthe LBs during accumulation of the LBs carrying the control informationfor a subframe at a receiver, thus decreasing the average interferencepower.

In accordance with an exemplary embodiment of the present invention,each UE generates its ZC sequence on an LB basis in a subframe andapplies a random sequence having a random phase or a random cyclic shiftvalue to the ZC sequence in each LB, thereby randomizing the ZCsequence. Then the UE transmits control information by the randomized ZCsequence. The random sequence is cell-specific. The interferencerandomization is further increased by use of a different random sequenceof phase values or cyclic shift values for each UE.

The present invention puts forth the following three methods. In thefollowing description, a ZC sequence of length N is denoted by g_(p)(n).The ZC sequence g_(p)(n) is randomized over M LBs and controlinformation is multiplied by the randomized ZC sequence g′_(p,m,k)(n)where k denotes the index of a channel carrying the control information.

Equation (2) describes the randomized ZC sequence according to Method 1.g′ _(p,m,k)(n)=g _(p)((n+d _(k))mod N)·S _(M,m),(m=1,2, . . . ,M,n=0,1,2, . . . ,N−1)  (2)where d_(k) denotes a cyclic shift value of the same ZC sequence, bywhich channel k carrying the control information is identified. Thecyclic shift value is preferably a time-domain cyclic shift valuealthough it can be a frequency-domain cyclic shift value. In equation(2), mod represents modulo operation. For instance, A mod B representsthe remainder of dividing A by B.

S_(M,m) is an orthogonal code of length M, being +1 s or −1 s. Thisorthogonal code can be a Walsh code where m denotes the index of an LBto which the control information is mapped. If the control informationis repeated four times in the slots of a subframe, the chips of a Walshsequence of length 4 are multiplied one to one by the LBs of each slot,and a combination of Walsh sequences for two slots in the subframe isdifferent for each cell, thus randomizing inter-cell interference. Foradditional randomization, a different combination of Walsh sequences canbe used for each UE.

Equation (3) describes the randomized ZC sequence according to Method 2.g′ _(p,m,k)(n)=g _(p)((n+d _(k))mod N)·e ^(jφ) ^(m) ,(m=1,2, . . . ,M,n=0,1,2, . . . ,N−1)  (3)where φ_(m) denotes a random phase value that changes the phase of theZC sequence g_(p)(n) in each LB. Inter-cell interference is randomizedby using different sets of random phase values, i.e. different randomphase sequences {φ_(m)} for adjacent cells in LBs of a subframe.

Equation (4) describes the randomized ZC sequence according to Method 3.g′ _(p,m,k)(n)=g _(p)((n+d _(k)+Δ_(m))mod N),(m=1,2, . . . ,M,n=0,1,2, . . . ,N−1)  (4)where Δ_(m) denotes a random cyclic shift value that changes thetime-domain cyclic shift value d_(k) of the ZC sequence g_(p)(n) in eachLB. Inter-cell interference is randomized by using different sets ofrandom time-domain cyclic shift values, i.e. different randomtime-domain cyclic shift sequences {Δ_(m)} for adjacent cells in LBs ofin a subframe. While the random cyclic shift values are used in the timedomain herein, they can be adapted to be used in the frequency domain.

Referring to FIG. 3, a UE receives sequence information and randomsequence information from a Node B by signaling in step 302. Thesequence information is about a ZC sequence for use in transmittingcontrol information, including the index of the ZC sequence and a cyclicshift value, and the random sequence information is used for randomizingthe ZC sequence, including a random phase sequence being a set of randomphase values or a random time-domain cyclic shift sequence being a setof random time-domain cyclic shift values, for application to LBs of asubframe. The signaling is upper-layer (e.g. L2) signaling or physicallayer (L1) signaling. To randomize inter-cell interference, the randomphase sequence or the random time-domain cyclic shift sequence isdifferent for each cell. For further interference randomization, therandom phase sequence or the random time-domain cyclic shift sequencecan also be set to be different for each UE.

In step 304, the UE generates control information and generatescomplex-valued modulation symbols (hereinafter, control symbols) usingthe control information. The number of the control symbols is equal tothat of LBs allocated for transmission of the control information. Forexample, if the control information is 1 bit, the UE creates as manycontrol symbols as the number of the allocated LBs by repetition.

In step 306, the UE generates the ZC sequence using the index and thecyclic shift value included in the sequence information. The UE thengenerates random values according to the random phase sequence or therandom time-domain cyclic shift sequence included in the random sequenceinformation in step 308. The random values are a Walsh sequence, randomphase values, or random time-domain cyclic shift values. These randomvalues are different for each cell and/or each UE. The UE generates arandomized ZC sequence by applying the random values to the ZC sequenceon an LB basis in step 310. In step 312, the UE multiplies therandomized ZC sequence by the control symbols, maps the products to theLBs, and transmits the mapped LBs.

Referring to FIG. 4, the Node B acquires a correlation signal bycorrelating a signal received from an intended UE in a plurality of LBswith a ZC sequence applied to the signal in step 402. In step 404, theNode B performs channel estimation on a pilot signal received from theUE and performs channel compensation for the correlation signal usingthe channel estimate. The Node B acquires control information byapplying random values corresponding to the UE to thechannel-compensated correlation signal on an LB basis and thus removingrandom values from the channel-compensated correlation signal in step406. The random values corresponding to the UE are known from randomsequence information that the Node B transmitted to the UE.

In the above transmission and reception of control information, an LB(i.e. an SC-FDMA symbol) is a basic unit to which the controlinformation is mapped for transmission. The ZC sequence is repeated inunits of LBs and the elements of the random phase sequence or the randomtime-domain cyclic shift sequence change LB by LB.

In the case where a plurality of cells exist under the same Node B, UEswithin each cell multiplex their control channels using the same ZCsequence and different time-domain cyclic shift values. If differentrandom phase sequences or random time-domain cyclic shift sequences areused on an LB basis in the cells of the Node B, orthogonality may belost among UEs. Under this environment, therefore, a random phasesequence or a random time-domain cyclic shift sequence is specific tothe Node B and the cells of the Node B use the same random sequence.

Embodiment 1

The first exemplary embodiment of the present invention implementsMethod 1 described in Equation (2).

Referring to FIG. 5, the same 1-bit control information occurs 8 timesin one subframe and is subject to frequency hopping on a slot basis inorder to achieve frequency diversity. If two SBs and the first and lastLBs carry pilots for channel estimation in each slot, the remaining LBsof the slot can be used for transmitting the control information. Whileone RU is used for transmitting the control information herein, aplurality of RUs can be used to support a plurality of users.

In a first slot, modulation symbols carrying the 1-bit controlinformation occur four times, for transmission in four LBs and aremultiplied by an orthogonal code of length 4, (S1 502 (=S1 _(4,1) S1_(4,2) S1 _(4,3) S1 _(4,4))) on an LB basis. S1 _(4,x) represents chip xof the orthogonal code S1. The pilot sequence is also multiplied by anorthogonal code of length 4, (S1′ 504 (=S1′_(4,1) S1′_(4,2) S1′_(4,3)S1′_(4,4))) on an LB or SB basis. The use of orthogonal codes canincrease the number of multiple-access users. For example, for length 4,four orthogonal codes are available. The use of the four orthogonalcodes enable four times more users to be accommodated in the sametime-frequency resources, as compared to non-use of orthogonal codes.

In a second slot, the 1-bit control information occurs four times and ismultiplied by an orthogonal code of length 4, [S2 506 (=S2 _(4,1)S_(4,2) S2 _(4,3) S2 _(4,4))] on an LB basis. The pilot sequence is alsomultiplied by an orthogonal code of length 4, (S2′ 508 (=S2′_(4,1)S2′_(4,2) S2′_(4,3) S2′_(4,4))) on an LB or SB basis.

The Node B signals orthogonal codes S1 502, S1′ 504, S2 506, and S2′ 508to the UE. Due to the nature of the orthogonal codes, their lengthsshould be multiples of 4. In FIG. 5, orthogonal codes of length 4 areapplied to each slot. If frequency hopping does not take place on a slotbasis in the transmission mechanism of FIG. 5, the control informationmay experience a negligibly small channel change in frequency duringone-subframe transmission. Therefore, orthogonality is still maintainedeven though the length of the orthogonal codes is extended to onesubframe. In this case, orthogonal codes of length 8 can be used fortransmitting the control information in one subframe.

A different combination of orthogonal codes to be applied to the slotsof one subframe is set for each cell to randomize inter-cellinterference. For example, for transmitting control information in theslots, Cell A uses orthogonal codes {S1, S2} sequentially and Cell Buses orthogonal codes {S3, S4} sequentially. The orthogonal codecombination {S3, S4} includes at least one different orthogonal codefrom the orthogonal code combination {S1,S2}.

Referring to FIG. 6A, the transmitter includes a controller 610, a pilotgenerator 612, a control channel signal generator 614, a data generator616, a Multiplexer (MUX) 617, a Serial-to-Parallel (S/P) converter 618,a Fast Fourier Transform (FFT) processor 619, a mapper 620, an InverseFast Fourier Transform (IFFT) 622, a Parallel-to-Serial (P/S) converter624, an orthogonal code generator 626, a multiplier 628, a Cyclic Prefix(CP) adder 630, and an antenna 632. Components and an operation relatedto UL data transmission are well known in the art and therefore, willnot be described herein.

Controller 610 provides overall control to the operation of thetransmitter and generates control signals required for MUX 617, FFTprocessor 619, mapper 620, pilot generator 612, control channel signalgenerator 614, data generator 616, and orthogonal code generator 626.The control signal provided to pilot generator 612 indicates a sequenceindex and a time-domain cyclic shift value by which to generate a pilotsequence. Control signals associated with UL control information anddata transmission are provided to control channel signal generator 614and data generator 616.

MUX 617 multiplexes a pilot signal, a data signal, and a control channelsignal received from pilot generator 612, data generator 616, andcontrol channel signal generator 614 according to timing informationindicated by a control signal received from controller 610, fortransmission in an LB or an SB. Mapper 620 maps the multiplexed signalto frequency resources according to LB/SB timing information andfrequency allocation information received from controller 610.

When only control information is transmitted without data, orthogonalcode generator 626 generates orthogonal codes for LBs/SBs according toinformation about cell-specific or UE-specific orthogonal codes to beused for slots, received from controller 610, and applies the chips ofthe orthogonal codes to the control symbols of the control channelsignal mapped to LBs according to timing information received fromcontroller 610. The orthogonal code information is provided tocontroller 610 by Node B signaling.

S/P converter 618 converts the multiplexed signal from MUX 617 toparallel signals and provides them to FFT processor 619. Theinput/output size of FFT processor 619 varies according to a controlsignal received from controller 610. Mapper 620 maps FFT signals fromFFT processor 619 to frequency resources. IFFT processor 622 convertsthe mapped frequency signals to time signals and P/S converter 624serializes the time signals. Multiplier 628 multiplies the serial timesignal by the orthogonal codes generated from orthogonal code generator626. That is, orthogonal code generator 626 generates orthogonal codesto be applied to the slots of a subframe that will carry the controlinformation according to the timing information received from controller610.

CP adder 630 adds a CP to the signal received from multiplier 628 toavoid inter-symbol interference and transmits the CP-added signalthrough transmit antenna 632.

Referring to FIG. 6B, a sequence generator 642 of control channel signalgenerator 614 generates a code sequence, for example, a ZC sequence onan LB basis. To do so, sequence generator 642 receives sequenceinformation such as a sequence length and a sequence index fromcontroller 610. The sequence information is known to both the Node B andthe UE.

A control information generator 640 generates a modulation symbol having1-bit control information and a repeater 643 repeats the control symbolto produce as many control symbols as the number of LBs allocated to thecontrol information. A multiplier 646 CDM-multiplexes the controlsymbols by multiplying the control symbols by the ZC sequence on an LBbasis, thus producing a control channel signal.

The multiplier 646 functions to generate the user-multiplexed controlchannel signal by multiplying the symbols output from the repeater 643by the ZC sequence. A modified embodiment of the present invention canbe contemplated by replacing the multiplier 646 with an equivalentdevice.

Referring to FIG. 7A, the receiver includes an antenna 710, a CP remover712, an S/P converter 714, an FFT processor 716, a demapper 718, an IFFTprocessor 720, a P/S converter 722, a Demultiplexer (DEMUX) 724, acontroller 726, a control channel signal receiver 728, a channelestimator 730, and a data demodulator and decoder 732. Components and anoperation associated with UL data reception are well known in the artand therefore, will not be described herein.

Controller 726 provides overall control to the operation of thereceiver. It also generates control signals required for DEMUX 724, IFFTprocessor 720, demapper 718, control channel signal receiver 728,channel estimator 730, and data demodulator and decoder 732. Controlsignals related to UL control information and data are provided tocontrol channel signal receiver 728 and data demodulator and decoder732. A control channel signal indicating a sequence index and atime-domain cyclic shift value is provided to channel estimator 730. Thesequence index and the time-domain cyclic shift value are used togenerate a pilot sequence allocated to the UE.

DEMUX 724 demultiplexes a signal received from P/S converter 722 into acontrol channel signal, a data signal, and a pilot signal according totiming information received from controller 726. Demapper 718 extractsthose signals from frequency resources according to LB/SB timinginformation and frequency allocation information received fromcontroller 726.

Upon receipt of a signal including control information from the UEthrough antenna 710, CP remover 712 removes a CP from the receivedsignal. S/P converter 714 converts the CP-free signal to parallelsignals and FFT processor 716 processes the parallel signals by FFT.After demapping in demapper 718, the FFT signals are converted to timesignals in IFFT processor 720. The input/output size of IFFT processor720 varies according to the control signal received form controller 726.P/S converter 722 serializes the IFFT signals and DEMUX 724demultiplexes the serial signal into the control channel signal, thepilot signal, and the data signal.

Channel estimator 730 acquires a channel estimate from the pilot signalreceived from DEMUX 724. Control channel signal receiver 728channel-compensates the control channel signal received from DEMUX 724by the channel estimate and acquires control information transmitted bythe UE. Data demodulator and decoder 732 channel-compensates the datasignal received from DEMUX 724 by the channel estimate and then acquiresdata transmitted by the UE based on the control information.

When only control information is transmitted without data on the UL,control channel signal receiver 728 acquires the control information inthe manner described with reference to FIG. 5.

Referring to FIG. 7B, control channel signal receiver 728 includes acorrelator 740 and a derandomizer 742. A sequence generator 744 ofcorrelator 740 generates a code sequence, for example, a ZC sequenceused for the UE to generate 1-bit control information. To do so,sequence generator 744 receives sequence information indicating asequence length and a sequence index from controller 726. The sequenceinformation is known to both the Node B and the UE.

A conjugator 746 calculates the conjugate consequence of the ZCsequence. A multiplier 748 CDM-demultiplexes the control channel signalreceived from DEMUX 724 by multiplying the control channel signal by theconjugate sequence on an LB basis. An accumulator 750 accumulates thesignal received from multiplier 748 for the length of the ZC sequence. Achannel compensator 752 channel-compensates the accumulated signal bythe channel estimate received from channel estimator 730.

In derandomizer 742, an orthogonal code generator 754 generatesorthogonal codes by which the UE uses in transmitting the 1-bit controlinformation, according to orthogonal code information. A multiplier 758multiplies the channel-compensated signal by the chips of the orthogonalsequences on an LB basis. An accumulator 760 accumulates the signalreceived from multiplier 758 for the number of LBs to which the 1-bitcontrol information was repeatedly mapped, thereby acquiring the 1-bitcontrol information. The orthogonal code information is signaled fromthe Node B to the UE so that both the Node B and the UE are aware of theorthogonal code information.

In a modified embodiment of the present invention, channel compensator752 is disposed between multiplier 758 and accumulator 760. Whilecorrelator 740 and derandomizer 742 are separately configured in FIG.7B, sequence generator 744 of correlator 740 and orthogonal codegenerator 754 of derandomizer 742 can be incorporated into a singledevice depending on a configuration method. For example, if correlator740 is configured so that sequence generator 744 generates a ZC sequencewith an orthogonal code applied on an LB basis for each UE, multiplier758 and orthogonal code generator 754 of derandomizer 742 are not used.Thus, a device equivalent to that illustrated in FIG. 7B is achieved.

Embodiment 2

The second exemplary embodiment of the present invention implementsMethod 2 described in Equation (3).

Referring to FIG. 8, one slot includes a total of 7 LBs and the fourthLB carries a pilot signal in each slot. Hence, one subframe has 14 LBsin total, and 2 LBs are used for pilot transmission and 12 LBs forcontrol information transmission. While one RU is used for transmittingcontrol information herein, a plurality of RUs can be used to support aplurality of users.

The same 1-bit control information occurs 6 times in each slot, thus 12times in one subframe. For frequency diversity, frequency hopping isperformed for the control information on a slot basis. A random phase isapplied to a ZC sequence in each LB carrying the control information.The resulting randomization of the ZC sequence randomizes inter-cellinterference.

Random phase values applied to the ZC sequence in LBs are φ₁, φ₂, . . ., φ₁₂ 802 to 824. The ZC sequence is multiplied by e^(jφ) ^(m) (m=1, 2,. . . , 12), thus being phase-rotated. As a random phase sequence, beinga set of random phase values for LBs is cell-specific; hence, theinter-cell interference is randomized. That is, since the correlationbetween randomized ZC sequences used for LBs of different cells israndomly phase-rotated over one subframe, interference between controlchannels from the cells is reduced.

The Node B signals the random phase sequence to the UE so that both areaware of the random phase sequence. To reduce the inter-cellinterference, a cell-specific random phase value can also be applied tothe pilot signal. The Node B signals the random phase value to the UE sothat both are aware of the random phase sequence.

Referring to FIG. 9, one slot includes a total of 6 LBs and 2 SBscarrying a pilot signal. Hence, one subframe has 12 LBs in total, and 4LBs are used for pilot transmission and 12 LBs for control informationtransmission. The same 1-bit control information occurs 6 times in eachslot, thus 12 times in one subframe. For frequency diversity, frequencyhopping is performed for the control information on a slot basis.

Referring to FIG. 10A, the transmitter includes a controller 1010, apilot generator 1012, a control channel signal generator 1014, a datagenerator 1060, a MUX 1017, an S/P converter 1018, an FFT processor1019, a mapper 1020, an IFFT 1022, a P/S converter 1024, a CP adder1030, and an antenna 1032. Components and an operation related to ULdata transmission are well known in the art and therefore, will not bedescribed herein.

Controller 1010 provides overall control to the operation of thetransmitter and generates control signals required for MUX 1017, FFTprocessor 1019, mapper 1020, pilot generator 1012, control channelsignal generator 1014, and data generator 1016. A control signalprovided to pilot generator 1012 indicates a sequence index indicatingan allocated pilot sequence and a time-domain cyclic shift value, forpilot generation. Control signals associated with UL control informationand data transmission are provided to control channel signal generator1014 and data generator 1016.

MUX 1017 multiplexes a pilot signal, a data signal, and a controlchannel signal received from pilot generator 1012, data generator 1016,and control channel signal generator 1014 according to timinginformation indicated by a control signal received from controller 1010,for transmission in an LB or an SB. Mapper 1020 maps the multiplexedinformation to frequency resources according to LB/SB timing informationand frequency allocation information received from controller 1010.

When only control information is transmitted without data, controlchannel signal generator 1014 generates a control channel signal byapplying a ZC sequence randomized on an LB basis to control informationin the afore-described method.

S/P converter 1018 converts the multiplexed signal from MUX 1017 toparallel signals and provides them to FFT processor 1019. Theinput/output size of FFT processor 1019 varies according to a controlsignal received from controller 1010. Mapper 1020 maps FFT signals fromFFT processor 1019 to frequency resources. IFFT processor 1022 convertsthe mapped frequency signals to time signals and P/S converter 1024serializes the time signals. CP adder 1030 adds a CP to the serialsignal and transmits the CP-added signal through transmit antenna 1032.

Referring to FIG. 10B, a sequence generator 1042 of control channelsignal generator 1014 generates a code sequence, for example, a ZCsequence to be used for LBs. A randomizer 1044 generates a random phasevalue for each LB and multiplies the random phase value by the ZCsequence in each LB. To do so, sequence generator 1042 receives sequenceinformation such as a sequence length and a sequence index fromcontroller 1010 and randomizer 1044 receives random sequence informationabout the random phase value for each LB from controller 1010. Then,randomizer 1044 rotates the phase of the ZC sequence by the random phasevalue in each LB, thus randomizing the phase of the ZC sequence. Thesequence information and the random sequence information are known toboth the Node B and the UE.

A control information generator 1040 generates a modulation symbolhaving 1-bit control information and a repeater 1043 repeats the controlsymbol to produce as many control symbols as the number of LBs allocatedto the control information. A multiplier 1046 CDM-multiplexes thecontrol symbols by multiplying the control symbols by the randomized ZCsequence on an LB basis, thus producing a control channel signal.

Multiplier 1046 functions to randomize the symbols output from repeater1043 by the randomized ZC sequence on a symbol basis. A modifiedembodiment of the present invention can be contemplated by replacingmultiplier 1046 with a device that performs a function equivalent toapplying or combining the randomized ZC sequence to or with the controlsymbols. For example, multiplier 1046 can be replaced with a phaserotator that changes the phases of the control symbols according to thephase values of the randomized ZC sequence, φ_(m) or Δ_(m).

Referring to FIG. 11A, the receiver includes an antenna 1110, a CPremover 1112, an S/P converter 1114, an FFT processor 1116, a demapper1118, an IFFT processor 1120, a P/S converter 1122, a DEMUX 1124, acontroller 1126, a control channel signal receiver 1128, a channelestimator 1130, and a data demodulator and decoder 1132. Components andan operation associated with UL data reception are well known in the artand therefore, will not be described herein.

Controller 1126 provides overall control to the operation of thereceiver. It also generates control signals required for DEMUX 1124,IFFT processor 1120, demapper 1118, control channel signal receiver1128, channel estimator 1130, and data demodulator and decoder 1132.Control signals related to UL control information and data are providedto control channel signal receiver 1128 and data demodulator and decoder1132. A control signal indicating a sequence index indicating a pilotsequence allocated to the UE and a time-domain cyclic shift value isprovided to channel estimator 1130. The sequence index and thetime-domain cyclic shift value are used for pilot reception.

DEMUX 1124 demultiplexes a signal received from P/S converter 1122 intoa control channel signal, a data signal, and a pilot signal according totiming information received from controller 1126. Demapper 1118 extractsthose signals from frequency resources according to LB/SB timinginformation and frequency allocation information received fromcontroller 1126.

Upon receipt of a signal including control information from the UEthrough antenna 1110, CP remover 1112 removes a CP from the receivedsignal. S/P converter 1114 converts the CP-free signal to parallelsignals and FFT processor 1116 processes the parallel signals by FFT.After processing in demapper 1118, the FFT signals are converted to timesignals in IFFT processor 1120. P/S converter 1122 serializes the IFFTsignals and DEMUX 1124 demultiplexes the serial signal into the controlchannel signal, the pilot signal, and the data signal.

Channel estimator 1130 acquires a channel estimate from the pilot signalreceived from DEMUX 1124. Control channel signal receiver 1128channel-compensates the control channel signal received from DEMUX 1124by the channel estimate and acquires the control information transmittedby the UE. Data demodulator and decoder 1132 channel-compensates thedata signal received from DEMUX 1124 by the channel estimate and thenacquires data transmitted by the UE based on the control information.

When only control information is transmitted without data on the UL,control channel signal receiver 1128 acquires the control information inthe manner described with reference to FIGS. 8 and 9.

Referring to FIG. 11B, control channel signal receiver 1128 includes acorrelator 1140 and a derandomizer 1142. A sequence generator 1144 ofcorrelator 1140 generates a code sequence, for example, a ZC sequenceused for the UE to generate control information. To do so, sequencegenerator 1144 receives sequence information indicating a sequencelength and a sequence index from controller 1126. The sequenceinformation is known to both the Node B and the UE.

A conjugator 1146 calculates the conjugate consequence of the ZCsequence. A multiplier 1148 CDM-demultiplexes the control channel signalreceived from DEMUX 1124 by multiplying the control channel signal bythe conjugate sequence on an LB basis. An accumulator 1150 accumulatesthe product signal for the length of the ZC sequence. Multiplier 1148 ofthe correlator 1140 can be replaced with a phase rotator that changesthe phases of the control channel signal on an LB basis according to thephase values d_(k) of the sequence received from sequence generator1144. A channel compensator 1152 channel-compensates the accumulatedsignal by the channel estimate received from channel estimator 1130.

In derandomizer 1142, a random value generator 1156 calculates theconjugate phase values of random phase values that the UE uses intransmitting the control information, according to random sequenceinformation. A multiplier 1158 multiplies the channel-compensated signalby the conjugate phase values on an LB basis. Like multiplier 1046 ofthe transmitter, multiplier 1158 of derandomizer 1142 can be replacedwith a phase rotator that changes the phases of the control channelsignal on an LB basis according to the phase values φ_(m) or Δ_(m) ofthe random sequence received from sequence generator 1156.

An accumulator 1160 accumulates the signal received from multiplier 1158for the number of LBs to which the 1-bit control information wasrepeatedly mapped, thereby acquiring the 1-bit control information. Therandom sequence information is signaled from the Node B to the UE sothat both are aware of the random sequence information.

In a modified embodiment of the present invention, channel compensator1152 is disposed between multiplier 1158 and accumulator 1160. Whilecorrelator 1140 and derandomizer 1142 are separately configured in FIG.11B, sequence generator 1144 of correlator 1140 and random valuegenerator 1156 of derandomizer 1142 can be incorporated into a singledevice depending on a configuration method. For example, if correlator1140 is configured so that sequence generator 1144 generates a ZCsequence to which a random sequence is applied for each UE, multiplier1158 and random value generator 1156 of derandomizer 1142 are not used.Thus, a device equivalent to that illustrated in FIG. 11B is achieved.In this case, like multiplier 1046 of the transmitter, multiplier 1148of correlator 1140 can be replaced with a phase rotator that changes thephases of the control channel signal on a symbol basis according to thephase values (d_(k)+φ_(m)) or (d_(k)+Δ_(m)) of the sequence receivedfrom sequence generator 1144.

Setting a different phase value for each LB to each UE can furtherincrease the inter-cell interference randomization. The Node B signalsthe phase value of each LB to each UE.

Aside from a random sequence as a phase sequence applied to 12 LBscarrying 1-bit control information, an orthogonal phase sequence such asa Fourier sequence can be used in the second exemplary embodiment of thepresent invention. A Fourier sequence of length N is defined as Equation(5):

$\begin{matrix}{{{f_{k}(n)} = {\mathbb{e}}^{{- j}\frac{2\pi\;{kn}}{N}}},\left( {{n = 0},\cdots\mspace{14mu},{N - 1},{k = 0},\cdots\mspace{14mu},{N - 1}} \right)} & (5)\end{matrix}$

In Equation (5), a different cell-specific value k is set for each cell.When phase rotation is performed on an LB basis using a differentFourier sequence for each cell, there is no interference among cells iftiming is synchronized among the cells.

The first and second exemplary embodiments can be implemented incombination. In the transmission mechanism of FIG. 5, LBs carrying 1-bitcontrol information are multiplied by an orthogonal code and then by arandom phase sequence. As the random phase sequence is cell-specific,the inter-cell interference is reduced.

Embodiment 3

The third exemplary embodiment of the present invention implementsMethod 3 described in Equation (4).

The time-domain cyclic shift value of a ZC sequence is cell-specific andchanges in each LB that carries control information, thereby randomizinginter-cell interference. To be more specific, a cell-specific cyclicshift value Am applied to each LB is further applied in the time domainin addition to a cyclic shift value d_(k) applied to each of controlchannels that are CDM-multiplexed in the same frequency resources withina cell. The Node B signals the cell-specific cyclic shift value to theUE. The cell-specific cyclic shift value is set to be larger than themaximum delay of a radio transmission path in order to keep theorthogonality of the ZC sequence.

To reduce the inter-cell interference, a cell-specific randomtime-domain cyclic shift value can also be applied to the pilot signal.The Node B signals the random time-domain cyclic shift value to the UEso that the random time-domain cyclic shift sequence is known to boththe Node B and the UE.

Referring to FIG. 12A, one slot includes a total of 7 LBs and the fourthLB carries a pilot signal in each slot. Hence, one subframe has 14 LBsin total, and 2 LBs are used for pilot transmission and 12 LBs forcontrol information transmission. While one RU is used for transmittingcontrol information herein, a plurality of RUs can be used to support aplurality of users.

Random time-domain cyclic shift values applied to the 12 LBs of the ZCsequence are Δ₁, Δ₂, . . . , Δ₁₂ 1202 to 1224. The ZC sequence iscyclically shifted by the random time-domain cyclic shift values 1202 to1224 on an LB basis to randomize the control information.

FIG. 12B is a detailed view of FIG. 12A. To CDM-multiplex differentcontrol channels within a cell, the same time-domain cyclic shift valued_(k) (k is a control channel index) applies to each LB, and torandomize interference between control information from adjacent cells,different cell-specific time-domain cyclic shift values 1202 to 1224apply to LBs. That is, the ZC sequence is additionally cyclicallyshifted by a time-domain cyclic shift value for each UE in the cell.Reference numerals 1230 and 1232 denote first and second slots,respectively in one subframe. For convenience' sake, frequency hoppingis not shown.

When a UE-specific time-domain cyclic shift is used for additionalrandomization, the time-domain cyclic shift values 1202 to 1224 indicatea UE-specific random sequence and the combination of d_(k) and thetime-domain cyclic shift values 1202 to 1224 maintains orthogonalityamong the control channels within the same cell.

FIG. 13 illustrates another transmission mechanism for controlinformation according to the third exemplary embodiment of the presentinvention. Time-domain cyclic shift values of a ZC sequence for 12 LBsare Δ₁, Δ₂, . . . , Δ₁₂ 1302 and 1324. The ZC sequence is cyclicallyshifted in each LB by a time-domain cyclic shift value in order torandomize control information.

A transmitter and a receiver according to the third exemplary embodimentof the present invention are identical in configuration to thoseillustrated in FIGS. 10A and 10B and FIGS. 11A and 11B, except that therandomizer 1044 illustrated in FIG. 10B randomizes a ZC sequence withrandom time-domain cyclic shifts on an LB basis and the random valuegenerator 1156 illustrated in FIG. 11B calculates the conjugate phasevalue of the random time-domain cyclic shift value of each LB andprovides it to the multiplier 1158.

The first and third exemplary embodiments can be implemented incombination. That is, in the transmission mechanism of FIG. 5, controlinformation is multiplied by an orthogonal code, and then additionallyby a random cyclic shift sequence on an LB basis as illustrated in FIG.12 or FIG. 13. As the random cyclic shift sequence is different for eachcell, the inter-cell interference is reduced.

As is apparent from the above description, the present inventionadvantageously reduces inter-cell interference by applying a randomphase or a cyclic shift value to each block on a cell basis or on a UEbasis, when UL control information from different users is multiplexedin a future-generation multi-cell mobile communication system.

While the invention has been shown and described with reference tocertain exemplary embodiments of the present invention thereof, they aremere exemplary applications. For example, the exemplary embodiments ofthe present invention are applicable to control information with aplurality of bits such as a CQI as well as 1-bit control information.Also, a random value for a code sequence used for control informationcan be applied in a predetermined resource block basis as well as on anLB basis. Thus, it will be understood by those skilled in the art thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope of the present invention as furtherdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for transmitting control information ina Single Carrier-Frequency Division Multiple Access (SC-FDMA) system,the method comprising the steps of: identifying by a User Equipment(UE), a cyclically shifted sequence by using a random cyclic shift valuebased on an SC-FDMA symbol index and a slot index; acquiring, by the UE,a control channel signal, combining the control information with thecyclically shifted sequence on an SC-FDMA symbol basis; andtransmitting, by the UE, the control channel signal in an SC-FDMA symbolto a Node B.
 2. The method of claim 1, wherein the control informationcomprises at least one of an ACK/NACK symbol and a pilot signal.
 3. Amethod for receiving control information in a Single Carrier-FrequencyDivision Multiple Access (SC-FDMA) system, the method comprising thesteps of: receiving, by a Node B, a control channel signal, includingthe control information, from a User Equipment (UE); identifying, by theNode B, a cyclically shifted sequence by using a random cyclic shiftvalue based on an SC-FDMA symbol index and a slot index; and acquiring,by the Node B, the control information from the control channel signalby using the cyclically shifted sequence.
 4. The method of claim 3,wherein the control information comprises at least one of an ACK/NACKsymbol and a pilot signal.
 5. An apparatus for transmitting controlinformation in a Single Carrier-Frequency Division Multiple Access(SC-FDMA) system, the apparatus comprising: a control channel signalgenerator for identifying a cyclically shifted sequence by using arandom cyclic shift value based on an SC-FDMA symbol index and a slotindex, and acquiring; a control channel signal, combining the controlinformation with the cyclically shifted sequence on an SC-FDMA symbolbasis; and a transmitter for transmitting the control channel signal inan SC-FDMA symbol to a Node B.
 6. The apparatus of claim 5, wherein thecontrol information comprises at least one of an ACK/NACK symbol and apilot signal.
 7. An apparatus for receiving control information in aSingle Carrier-Frequency Division Multiple Access (SC-FDMA) system,comprising: a receiver for receiving a control channel signal, includingcontrol information, from a User Equipment (UE); and a control channelsignal receiver for identifying a cyclically shifted sequence by using arandom cyclic shift value based on an SC-FDMA symbol index and a slotindex, and acquiring the control information from the control channelsignal by using the cyclically shifted sequence.
 8. The apparatus ofclaim 7, wherein the control information comprises at least one of anACK/NACK symbol and a pilot signal.